<!DOCTYPE html>
<html lang="zh-CN">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0, maximum-scale=1,minimum-scale=1, user-scalable=no">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <script src="https://cdn.bootcss.com/jquery/3.4.1/jquery.min.js"></script>
    <style>
        *{ margin: 0; padding: 0; touch-action: pan-y;}
        html, body{ width: 100%; height: 100%;; position: relative; overflow: hidden; }
        #box{ width: 300px; height: 300px; position: absolute; background-color: black; }
    </style>
    <title>手机端缩放</title>
</head>
<body>
    
    <div id="box"></div>
    <script>
        function setGesture(el){
            var obj={}; //定义一个对象
            var istouch=false;
            var start=[];
            var scale = null;
            var rotation = null;
            el.addEventListener("touchstart",function(e){
                if(e.touches.length>=2){  //判断是否有两个点在屏幕上
                    istouch=true;
                    start=e.touches;  //得到第一组两个点
                    obj.gesturestart&&obj.gesturestart.call(el,e); //执行gesturestart方法
                };
            },false);
            document.addEventListener("touchmove",function(e){
                e.preventDefault();
                if(e.touches.length>=2&&istouch){
                    console.log(1);
                    var now=e.touches;  //得到第二组两个点
                    scale=getDistance(now[0],now[1])/getDistance(start[0],start[1]); //得到缩放比例，getDistance是勾股定理的一个方法
                    rotation=getAngle(now[0],now[1])-getAngle(start[0],start[1]);  //得到旋转角度，getAngle是得到夹角的一个方法
                    e.scale=scale.toFixed(2);
                    e.rotation=rotation.toFixed(2);
                    obj.gesturemove&&obj.gesturemove.call(el,e);  //执行gesturemove方法
                };
            },false);
            document.addEventListener("touchend",function(e){
                if(istouch){
                    istouch=false;
                    obj.gestureend&&obj.gestureend.call(el,e);  //执行gestureend方法
                };
            },false);
            return obj;
        };
        function getDistance(p1, p2) {
            var x = p2.pageX - p1.pageX,
                y = p2.pageY - p1.pageY;
            return Math.sqrt((x * x) + (y * y));
        };
        function getAngle(p1, p2) {
            var x = p1.pageX - p2.pageX,
                y = p1.pageY- p2.pageY;
            return Math.atan2(y, x) * 180 / Math.PI;
        };

        var box=document.querySelector("#box");
        var boxGesture=setGesture(box);  //得到一个对象
        boxGesture.gesturestart=function(e){  //双指开始
            box.style.backgroundColor="yellow";
            box.style.transform="scale("+e.scale+") rotate("+e.rotation+"deg)";//改变目标元素的大小和角度
        };
        boxGesture.gesturemove=function(e){  //双指移动
            box.innerHTML = e.scale+"<br />"+e.rotation;
            box.style.transform="scale("+e.scale+") rotate("+e.rotation+"deg)";//改变目标元素的大小和角度
        };
        boxGesture.gestureend=function(e){  //双指结束
            box.innerHTML="";
            box.style.cssText="background-color:red";
            box.style.transform="scale("+e.scale+") rotate("+e.rotation+"deg)";//改变目标元素的大小和角度
        };
    </script>
</body>
</html>